762 H. E. KNow.tTon 
a weak aniline-blue solution brings them out more clearly. In pollen tubes 
of apple, the plugs are more numerous than in Antirrhinum. 
The germination of Antirrhinum pollen was greatly stimulated by the 
addition of a minute amount of the crushed stigma of Antirrhinum. 
Pollen in a sugar solution showed germ tubes appearing after one and 
one-half hours. The addition of a piece of the stigma to the same 
concentration of sugar so stimulated germination that within one 
hour the germ tubes were from one to four times the diameter of 
the grains in length. Marked chemotropism also resulted, the germ 
tubes growing toward, and even penetrating, the stigma tissue. No 
effect was obtained by the addition of either geranium or petunia 
stigmas, however. 
Even pollen from anthers that had not denisced was germinated. 
Pollen from anthers which would have dehisced three days later showed 
no germination after two hours, in contrast to mature pollen, which 
showed a 60-per-cent germination. After twenty hours, the immature 
pollen showed a 65-per-cent germination, while the mature pollen gave an 
85-per-cent germination. The germ tubes of the mature pollen were 
longer. A small percentage of germination was obtained with more 
immature pollen, but it was very slow and weak. Very immature grains, 
below normal in size, seemed to grow larger when placed in a nutrient 
solution, but no germination tock place. Jt is apnarent, then, that pollen 
matures several days before the anthers dehisce. 
Optimum temperatures for Antirrhinum-pollen germination were deter- 
mined. The pollen was taken from the same anther. The results, given 
in table 3, are the averages of six cultures for each temperature, the media 
being cane-sugar solutions: 
TABLE 3. ANTIRRHINUM POLLEN GERMINATION AT DIFFERENT TEMPERATURES 
Memperature;(Centiprade)) 92. css eo ee ae Pile 33° 
Germination (per cent). 18 2. aces ness scalar 36 
Under the conditions of the experiment, it may be concluded that the 
optimum temperature for the germination of Antirrhinum pollen is 
about 25° C, 
